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DO189-1
TA133-User’s Guide
IEC Measurement Categories
Definitions and Examples (Clause 6.5.2)
Measurement Category I
Definition:
Measurement category I is for measurements performed
on circuits not directly connected to a mains supply.
Examples:
Measurements in circuits not derived from a mains supply
and specially protected ( internal ) circuits derived
from a mains supply. In the latter case, transient stresses
are variable; for that reason it is required that the
transient withstand capability of the equipment is made
known to the user.
Measurement Category II
Definition:
Measurement category II is for measurements performed
CAT II
on circuits directly connected to the low voltage
installation.
Examples:
Household appliances, portable tools and similar
equipment.
Measurement Category III
Definition:
Measurement category III is for measurements
CAT III
performed in the building installation.
Examples:
Measurements on distribution boards, circuit breakers,
wiring including cables, bus-bars, junction boxes, switches,
socket-outlets in the fixed installation and equipment for
industrial use like for example stationary motors with per-
manent connection to the fixed installation.
Measurement Category IV
Definition:
Measurement category IV is for measurements
CAT IV
performed at the source of the low-voltage installation.
Examples:
Electricity meters and measurements on primary over
current protection devices and and ripple control units.